# ISEE Upper Level Math : How to find the radius of a sphere

## Example Questions

### Example Question #1 : How To Find The Radius Of A Sphere

A wooden ball has a surface area of .

Cannot be determined from the information provided

Explanation:

A wooden ball has a surface area of .

Begin with the formula for surface area of a sphere:

Now, plug in our surface area and solve with algebra:

Get rid of the pi

Divide by 4

Square root both sides to get our answer:

### Example Question #2 : How To Find The Radius Of A Sphere

There is a perfectly spherical weather balloon with a surface area of  , what is its radius?

Explanation:

There is a perfectly spherical weather balloon with a surface area of  , what is its radius?

Begin with the formula for surface area of a sphere:

Now, set it equal to the given surface area and solve for r:

First divide both sides by .

Then square root both sides to get our answer: